Many farmers and some state officials believe the increased crude oil and freight shipments from North Dakota's booming oil patch were largely the cause of shipping delays, which have created big backlogs at grain elevators and added costs for agriculture shippers.

But BNSF Railway Co. and Canadian Pacific Railway officials told the North Dakota Public Service Commission during a meeting with representative from agriculture and transportation groups that brutal winter weather and bottlenecks in Chicago are to blame.

"It's hard to explain just how bad weather affects a rail system," said Brian Sweeney, a BNSF vice president.

Commissioner Randy Christmann told railroad officials that regulators have been "bombarded" by farm groups to push the railroad to improve its service in North Dakota.

"People are expecting us to solve this problem," Christmann said of the commission, which regulates coal mining, land reclamation, pipelines, electric and gas utilities, grain elevators, telecommunications and auctioneers. "There is a perception that oil traffic is displacing ag traffic and that's causing an enormous amount of loses for producers."

Grain bins across the state are full and harvests from prior years are being stored on the ground, North Dakota Grain Growers Association executive director Dan Wogsland said, noting Montana, South Dakota and Minnesota are having similar problems.

"We've got to continue to ship ag in North Dakota," he said. "It was here before the oil play and it's going to be here after the oil play."

Canadian Pacific says its backlogs should be down in a few weeks and BNSF predicts it'll be caught up by August.

Railroad officials told the three-member committee that a rebounding national economy also has contributed to congestion problems. Sweeney said intermodal, which refers to shipping containers that are moved from ships, and coal shipments have gone up with increased grain and crude oil rail demand.

"It's not just one culprit causing the problem," Sweeney said.

BNSF Marketing Director Jonathan Long said oil shippers have told railroad officials that they believe the railroad has given priority to farm commodity shipments.

"They are accusing us of giving ag preference," he said.

BNSF has promised to add more locomotives and crews in an effort to address agriculture shipping delays.

"The problem you are experiencing in North Dakota is not unique," Sweeney said. "It's broad-based across the system."

Canadian Pacific spokesman Herb Jones said the Calgary-based railroad does not plan to add trains or crews to address the backlog, again pointing the finger at congestion at the Chicago, the nation's biggest rail hub.